STUDY ON THE CONSTRAINT EFFECT USING THE DAMAGE MECHANICS APPROACH.

(1)通过改变约束条件，进行断裂韧性测试。断裂韧性值是一个宏观参数，受约束条件的影响。通过扫描电子显微镜（SEM）断口观察发现，韧窝直径、韧窝个数、功率值等微观参数也受约束条件的影响较大。（2）对不同缺口半径的缺口试样进行了韧窝断裂试验。断口观察表明，应力三轴性也强烈影响韧窝断裂过程。应力三轴度的变化意味着约束条件的变化。对凹坑直径和凹坑深宽比进行精确测量，获得3000多个数据。是本研究领域数据库的基础。(3)考虑损伤力学效应,采用有限元法进行韧窝断裂模拟。使用此代码模拟 (1) 和 (2) 中描述的两种测试。表明约束效果评价良好。使用此代码可以考虑基础矩阵中夹杂物非均匀分布的影响。显而易见，夹杂物的不均匀分布对韧窝断裂模式影响很大。(4)由此，约束条件与微观韧性断裂过程之间的关系逐渐清晰，这是从微观断裂力学角度研究约束条件的基础。

(1) By changing the constraint condition, fracture toughness tests are conducted. The fracture toughness value, which is a macroscopic parameter, is affected by the constraint condition. By the observation of fracture surface using scanning electron microscope(SEM), it was shown that the microscopic parameter such as dimple diameter, dimple number and power value are also affected by the constraint condition largely.(2) The dimple fracture tests of notched specimen with different notch radius are conducted. The fracture surface observation showed that the stress triaxiality also affects the dimple fracture process strongly. The change of the stress triaxiality means the change of the constraint condition. Precise measurement of the dimple diameter and dimple aspect ratio is made, and more than 3000 data are obtained. It is base of the data-base on this research area.(3) The dimple fracture simulation is conducted using FEM considering the damage mechanics effect. Two kinds of tests described in (1) and (2) are simulated using this code. It is shown that the constraint effect was evaluated well. The effect of the non-uniform distributions of inclusions in the base matrix can be considered using this code. It became obvious that the non-uniform distribution of inclusions affects the dimple fracture pattern largely.(4) As a result, the relation between the constraint condition and the microscopic ductile fracture process is becoming clear, which is the basis of the study on the constraint condition from the microscopic fracture mechanics.